Lithographic apparatus and device manufacturing method

ABSTRACT

A lithographic projection apparatus includes a support structure configured to hold a patterning device, the patterning device configured to pattern a beam of radiation according to a desired pattern; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; a liquid supply system configured to provide liquid to a space between the projection system and the substrate; and a shutter configured to isolate the space from the substrate or a space to be occupied by a substrate.

This is application is a divisional of U.S. patent application Ser. No.12/796,482, filed Jun. 8, 2010, which is a continuation application ofU.S. patent application Ser. No. 11/499,780, filed Aug. 7, 2006, nowU.S. Pat. No. 7,932,999, which is a divisional application of U.S.patent application Ser. No. 10/831,370, filed Apr. 26, 2004, now U.S.Pat. No. 7,110,081, which is a continuation-in-part patent applicationof U.S. patent application Ser. No. 10/705,785, filed Nov. 12, 2003, nowU.S. Pat. No. 7,075,616, and claims priority from European patentapplications EP 02257822.3, filed Nov. 12, 2002, EP 03253636.9, filedJun. 9, 2003, and EP 03254059.3, filed Jun. 26, 2003, each of theforegoing applications herein incorporated in its entirety by reference.

FIELD

The present invention relates to immersion lithography.

BACKGROUND

The term “patterning device” as here employed should be broadlyinterpreted as referring to means that can be used to endow an incomingradiation beam with a patterned cross-section, corresponding to apattern that is to be created in a target portion of the substrate; theterm “light valve” can also be used in this context. Generally, the saidpattern will correspond to a particular functional layer in a devicebeing created in the target portion, such as an integrated circuit orother device (see below). Examples of such a patterning device include:

-   -   A mask. The concept of a mask is well known in lithography, and        it includes mask types such as binary, alternating phase-shift,        and attenuated phase-shift, as well as various hybrid mask        types. Placement of such a mask in the radiation beam causes        selective transmission (in the case of a transmissive mask) or        reflection (in the case of a reflective mask) of the radiation        impinging on the mask, according to the pattern on the mask. In        the case of a mask, the support structure will generally be a        mask table, which ensures that the mask can be held at a desired        position in the incoming radiation beam, and that it can be        moved relative to the beam if so desired.    -   A programmable mirror array. One example of such a device is a        matrix-addressable surface having a viscoelastic control layer        and a reflective surface. The basic principle behind such an        apparatus is that (for example) addressed areas of the        reflective surface reflect incident light as diffracted light,        whereas unaddressed areas reflect incident light as undiffracted        light. Using an appropriate filter, the said undiffracted light        can be filtered out of the reflected beam, leaving only the        diffracted light behind; in this manner, the beam becomes        patterned according to the addressing pattern of the        matrix-addressable surface. An alternative embodiment of a        programmable mirror array employs a matrix arrangement of tiny        mirrors, each of which can be individually tilted about an axis        by applying a suitable localized electric field, or by employing        piezoelectric actuation means. Once again, the mirrors are        matrix-addressable, such that addressed mirrors will reflect an        incoming radiation beam in a different direction to unaddressed        mirrors; in this manner, the reflected beam is patterned        according to the addressing pattern of the matrix-addressable        mirrors. The required matrix addressing can be performed using        suitable electronic means. In both of the situations described        hereabove, the patterning device can comprise one or more        programmable mirror arrays. More information on mirror arrays as        here referred to can be gleaned, for example, from United States        Patents U.S. Pat. No. 5,296,891 and U.S. Pat. No. 5,523,193, and        PCT patent applications WO 98/38597 and WO 98/33096, which are        incorporated herein by reference. In the case of a programmable        mirror array, the said support structure may be embodied as a        frame or table, for example, which may be fixed or movable as        required.    -   A programmable LCD array. An example of such a construction is        given in United States Patent U.S. Pat. No. 5,229,872, which is        incorporated herein by reference. As above, the support        structure in this case may be embodied as a frame or table, for        example, which may be fixed or movable as required.

For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table; however, the general principles discussed in such instancesshould be seen in the broader context of the patterning device ashereabove set forth.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs). In such a case, the patterningdevice may generate a circuit pattern corresponding to an individuallayer of the IC, and this pattern can be imaged onto a target portion(e.g. comprising one or more dies) on a substrate (silicon wafer) thathas been coated with a layer of radiation-sensitive material (resist).In general, a single wafer will contain a whole network of adjacenttarget portions that are successively irradiated via the projectionsystem, one at a time. In current apparatus, employing patterning by amask on a mask table, a distinction can be made between two differenttypes of machine. In one type of lithographic projection apparatus, eachtarget portion is irradiated by exposing the entire mask pattern ontothe target portion at one time; such an apparatus is commonly referredto as a wafer stepper. In an alternative apparatus—commonly referred toas a step-and-scan apparatus—each target portion is irradiated byprogressively scanning the mask pattern under the projection beam in agiven reference direction (the “scanning” direction) while synchronouslyscanning the substrate table parallel or anti-parallel to thisdirection; since, in general, the projection system will have amagnification factor M (generally <1), the speed V at which thesubstrate table is scanned will be a factor M times that at which themask table is scanned. More information with regard to lithographicdevices as here described can be gleaned, for example, from UnitedStates Patent U.S. Pat. No. 6,046,792, incorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (resist).Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. anIC. Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation,chemo-mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4, incorporated herein by reference.

For the sake of simplicity, the projection system may hereinafter bereferred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in United States Patent U.S. Pat.No. 5,969,441 and PCT patent application WO 98/40791, incorporatedherein by reference.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water so as to fill a space between the final element of theprojection system and the substrate. The point of this is to enableimaging of smaller features as the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.)

However, submersing the substrate or substrate and substrate table in abath of liquid (see for example United States Patent U.S. Pat. No.4,509,852, hereby incorporated in its entirety by reference) may meanthat there is a large body of liquid that must be accelerated during ascanning exposure, This may require additional or more powerful motorsand turbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application WO 99/49504, hereby incorporatedin its entirety by reference. As illustrated in FIGS. 9 and 10, liquidis supplied by at least one inlet IN onto the substrate, preferablyalong the direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 9 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 9 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and out-lets positioned around the finalelement are possible, one example is illustrated in FIG. 10 in whichfour sets of an inlet with an outlet on either side are provided in aregular pattern around the final element.

SUMMARY

With such and other arrangements for providing liquid on only alocalized area of the substrate, the substrate itself acts to containthe liquid of the liquid supply system in a space between the finalelement of the projection system and the substrate. If the substrate isremoved (for example, during substrate exchange) and no other measuresare taken, the liquid will run out of the liquid supply system. Clearlythis is a situation which is to be avoided, The liquid can be removedfrom the space before the substrate is moved. However, as the residue ofliquid which is inevitably left behind when the liquid supply system isemptied of liquid, dries, drying spots may be left behind on elements ofthe projection system which were immersed in the liquid during exposure.This may be clearly detrimental to the continuing high performance ofthe projection system. Also, on refilling the space with liquid, it maybe hard to avoid the formation of bubbles. Filling of the space withliquid will also take time and may reduce throughput time.

Accordingly, it may be advantageous to provide, for example, alithographic projection apparatus in which immersion lithography can beperformed and in which removing liquid from the liquid supply systemduring substrate exchange can be avoided or reduced.

According to an aspect, there is provided a lithographic projectionapparatus comprising:

a support structure configured to hold a patterning device, thepatterning device configured to pattern a beam of radiation according toa desired pattern;

a substrate table configured to hold a substrate;

a projection system configured to project the patterned beam onto atarget portion of the substrate;

a liquid supply system configured to provide an immersion liquid,through which said beam is to be projected, in a space between saidprojection system and said substrate; and

a shutter configured to keep said projection system in contact withliquid when said substrate is moved away from under said projectionsystem.

In this way drying marks on the projection system can be avoided. Thissolution is ideal for a localized area liquid supply system whichprovides immersion liquid to only a localized area of the substrate. Onearrangement could involve one or more jets to project liquid onto theprojection system during substrate swap.

In an embodiment, there is provided a shutter positionable on a side ofsaid liquid supply system opposite said projection system such thatliquid can be confined in said liquid supply system and between saidprojection system and said shutter. With this arrangement, for example,the shutter can be moved under the liquid supply system after exposureof the substrate in order to contain the immersion liquid. The substratemay then be moved from the substrate table without substantially losingliquid from the liquid supply system, because the shutter takes theplace of the substrate and is of a size equal to or greater than thelocalized area so that liquid can't substantially escape between theprojection system and the shutter.

In an embodiment, the shutter comprises a surface of said substratetable. With this arrangement, the substrate table is moved afterexposure to a position at which the substrate may be removed but also toa position at which the shutter is positioned over the liquid supplysystem. A seal, such as a gas seal, which can also be used to seal aliquid confinement structure that extends along at least a part of theboundary of said space to contain liquid and that forms an aperture forsaid patterned beam to pass through to the substrate during exposure,can remain activated to seal between the liquid supply system and theshutter. The shutter blocks the aperture. Alternatively, the shutter maybe raised relative to the structure to abut the structure and the sealcan then be de-activated.

In an embodiment, the shutter is separable from the remainder of theapparatus. It is also movable relative to the remainder of theapparatus. That is, the shutter is relatively small, perhaps shaped likea plate, and not permanently attached to other parts of the apparatus.In this embodiment, the substrate table can be moved completely awayfrom the liquid supply system after exposure as the shutter ispositioned over the liquid supply system and is independent of thesubstrate table. In this embodiment the shutter can be carried by thesubstrate table during exposure and to this end the shutter and/or thesubstrate table has or have a holding device configured to releasablyhold the shutter to the substrate table. Also, an attachment device maybe provided to releasably attach the shutter to the liquid supplysystem. The attachment device or the holding device may comprise amagnet to generate the force required to attach or hold. Alternatively,those devices may comprise a vacuum outlet configured to attract theshutter to the substrate table and/or the liquid supply system. In thecase of the attachment device, use may be made of a gas seal configuredto seal between the liquid supply system and the substrate duringexposure in order to provide the force to attach the shutter to theliquid supply system.

In an embodiment, the liquid supply system comprises an outletconfigured to remove liquid from the space and a gas inlet configured toprovide flushing gas in said space. Flushing might be required every nowand again due to contamination of the liquid or perhaps during a longterm shut down of the apparatus. In this way, liquid may be removed fromthe space and the space can be flushed with gas. The shutter is thenattached to the aperture to protect the projection system.

In an embodiment, the liquid supply system is configured to provide saidliquid to a space between a final lens of said projection system andsaid substrate.

According to an aspect, there is provided a device manufacturing methodcomprising:

providing an immersion liquid to a space between a projection system anda substrate;

projecting a patterned beam of radiation, through said liquid, onto atarget portion of the substrate using the projection system; and

maintaining said projection system in contact with liquid after saidsubstrate has been moved away from under said projection system.

Although specific reference may be made in this text to the use of theapparatus described herein in the manufacture of ICs, it should beexplicitly understood that such an apparatus has many other possibleapplications. For example, it may be employed in the manufacture ofintegrated optical systems, guidance and detection patterns for magneticdomain memories, liquid-crystal display panels, thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “reticle”, “wafer”or “die” in this text should be considered as being replaced by the moregeneral terms “mask”, “substrate” and “target portion”, respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in which:

FIG. 1 depicts a lithographic projection apparatus according to anembodiment of the invention;

FIG. 2 depicts the liquid reservoir of a first embodiment of theinvention;

FIG. 3 depicts the liquid reservoir and substrate table of the firstembodiment of the invention;

FIG. 4 depicts the liquid reservoir, substrate table and shutter memberof a second embodiment of the invention;

FIG. 5 depicts the liquid reservoir, substrate table and shutter memberof the second embodiment of the present invention;

FIG. 6 illustrates an alternative arrangement of the second embodimentof liquid reservoir, substrate table and shutter member of the presentinvention;

FIG. 7 illustrates a third embodiment of the present invention;

FIG. 8 illustrates a variant of the third embodiment;

FIG. 9 illustrates an alternative liquid supply system according to anembodiment of the invention;

FIG. 10 illustrates, in plan, the system of FIG. 9;

FIG. 11 depicts the liquid reservoir, substrate table and shutter memberof a fourth embodiment of the present invention;

FIG. 12 illustrates an alternative arrangement of the fourth embodimentof liquid reservoir, substrate table and shutter member of the presentinvention;

FIG. 13 illustrates a top view of a shutter member according to a fifthembodiment of the present invention;

FIG. 14 illustrates a side view of a shutter member according to a fifthembodiment of the present invention;

FIG. 15 illustrates a top view of a shutter member according to a fifthembodiment of the present invention; and

FIG. 16 illustrates a simplified layout of part of an immersionlithographic projection apparatus according to a sixth embodiment of thepresent invention.

In the Figures, corresponding reference symbols indicate correspondingparts.

DETAILED DESCRIPTION

Embodiment 1

FIG. 1 schematically depicts a lithographic projection apparatusaccording to a particular embodiment of the invention. The apparatuscomprises:

-   -   a radiation system Ex, IL, for supplying a projection beam PB of        radiation (e.g. UV radiation), which in this particular case        also comprises a radiation source LA;    -   a first object table (mask table) MT provided with a mask holder        for holding a mask MA (e.g. a reticle), and connected to first        positioning means for accurately positioning the mask with        respect to item PL;    -   a second object table (substrate table) WT provided with a        substrate holder for holding a substrate W (e.g. a resist-coated        silicon wafer), and connected to second positioning means for        accurately positioning the substrate with respect to item PL;    -   a projection system (“lens”) PL (e.g. a refractive lens system)        for imaging an irradiated portion of the mask MA onto a target        portion C (e.g. comprising one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive (e.g. has atransmissive mask). However, in general, it may also be of a reflectivetype, for example (e.g. with a reflective mask). Alternatively, theapparatus may employ another kind of patterning device, such as aprogrammable mirror array of a type as referred to above.

The source LA (e.g. an excimer laser) produces a beam of radiation. Thisbeam is fed into an illumination system (illuminator) IL, eitherdirectly or after having traversed conditioning means, such as a beamexpander Ex, for example. The illuminator IL may comprise adjustingmeans AM for setting the outer and/or inner radial extent (commonlyreferred to as σ-outer and σ-inner, respectively) of the intensitydistribution in the beam. In addition, it will generally comprisevarious other components, such as an integrator IN and a condenser CO.In this way, the beam PB impinging on the mask MA has a desireduniformity and intensity distribution in its cross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g. withthe aid of suitable directing mirrors); this latter scenario is oftenthe case when the source LA is an excimer laser. The current inventionand claims encompass both of these scenarios.

The beam PB subsequently intercepts the mask MA, which is held on a masktable MT. Having been selectively reflected by the mask MA, the beam PBpasses through the lens PL, which focuses the beam PB onto a targetportion C of the substrate W. With the aid of the second positioningmeans (and interferometric measuring means IF), the substrate table WTcan be moved accurately, e.g. so as to position different targetportions C in the path of the beam PB. Similarly, the first positioningmeans can be used to accurately position the mask MA with respect to thepath of the beam PB, e.g. after mechanical retrieval of the mask MA froma mask library, or during a scan. In general, movement of the objecttables MT, WT will be realized with the aid of a long-stroke module(course positioning) and a short-stroke module (fine positioning), whichare not explicitly depicted in FIG. 1. However, in the case of a waferstepper (as opposed to a step-and-scan apparatus) the mask table MT mayjust be connected to a short stroke actuator, or may be fixed.

The depicted apparatus can be used in two different modes:

1. In step mode, the mask table MT is kept essentially stationary, andan entire mask image is projected at one time (i.e. a single “flash”)onto a target portion C. The substrate table WT is then shifted in the xand/or y directions so that a different target portion C can beirradiated by the beam PB;

2. In scan mode, essentially the same scenario applies, except that agiven target portion C is not exposed in a single “flash”. Instead, themask table MT is movable in a given direction (the so-called “scandirection”, e.g. the y direction) with a speed v, so that the projectionbeam PB is caused to scan over a mask image; concurrently, the substratetable WT is simultaneously moved in the same or opposite direction at aspeed V=Mv, in which M is the magnification of the lens PL (typically,M=¼ or ⅕). In this manner, a relatively large target portion C can beexposed, without having to compromise on resolution.

FIG. 2 shows a liquid reservoir 10 between the projection system PL andthe substrate W which is positioned on the substrate stage WT. Theliquid reservoir 10 is filled with a liquid 11 having a relatively highrefractive index, e.g. water, provided via inlet/outlet ducts 13. Theliquid has the effect that the radiation of the projection beam is ashorter wavelength in the liquid than in air or in a vacuum, allowingsmaller features to be resolved. It is well known that the resolutionlimit of a projection system is determined, inter alia, by thewavelength of the projection beam and the numerical aperture of thesystem. The presence of the liquid may also be regarded as increasingthe effective numerical aperture. Furthermore, at fixed numericalaperture, the liquid is effective to increase the depth of focus.

The reservoir 10 forms, in an embodiment, a contactless seal to thesubstrate W around the image field of the projection lens PL so that theliquid is confined to fill the space between the substrate's primarysurface, which faces the projection system PL, and the final opticalelement of the projection system PL. The reservoir is formed by a sealmember 12 positioned below and surrounding the final element of theprojection lens PL. Thus, the liquid supply system provides liquid ononly a localized area of the substrate. The seal member 12 forms part ofthe liquid supply system for filling the space between the final elementof the projection system and the substrate W with a liquid. This liquidis brought into the space below the projection lens and within the sealmember 12. The seal member 12 extends a little above the bottom elementof the projection lens and the liquid rises above the final element sothat a buffer of liquid is provided. The seal member 12 has an innerperiphery that at the upper end closely conforms to the shape of theprojection system or the final elements thereof and may, e.g. be round.At the bottom the inner periphery forms an aperture which closelyconforms to the shape of the image field, e.g. rectangular, though thisis not necessarily so. The projection beam passes through this aperture.

The liquid 11 is confined in the reservoir 10 by a seal 16. Asillustrated in FIG. 2, the seal is a contactless seal, i.e. a gas seal.The gas seal is formed by gas, e.g. air or synthetic air, provided underpressure via inlet 15 to the gap between seal member 12 and substrate Wand extracted by first outlet 14. The over pressure on the gas inlet 15,vacuum level on the first outlet 14 and the geometry of the gap arearranged so that there is a high-velocity gas flow inwards towards theoptical axis of the apparatus that confines the liquid 11. As with anyseal, some liquid is likely to escape, for example up the first outlet14.

FIGS. 9 and 10 also depict a liquid reservoir defined by inlet(s) IN,outlet(s) OUT, the substrate W and the final element of projection lensPL. Like the liquid supply system of FIG. 2 the liquid supply systemillustrated in FIGS. 9 and 10, comprising inlet(s) IN and outlet(s) OUT,supplies liquid to a space between the final element of the projectionsystem and a localized area of the primary surface of the substrate.

As can be seen from FIGS. 2 and 9, during exposure, the substrate Wprovides the bottom wall of the liquid reservoir thereby containing theliquid in a space between the projection system PL and the substrate W.

FIG. 3 shows the substrate table WT according to a first embodimentwhich can be used to avoid the necessity of emptying liquid from theliquid reservoir once the substrate W has been imaged and before beingunloaded from the substrate table WT. A shutter member 100 (also termeda cover plate, edge seal member, gap seal means or member orintermediary plate) is provided for this purpose. The shutter member 100is a surface other than a substrate surface, in this case an upper (asillustrated) primary surface of the substrate table WT which issubstantially co-planar with the upper primary surface of the substrateW and is closely adjacent to the edge of the substrate W. The area ofthe shutter member 100 is large enough so that if the substrate table WTis moved such that the projection system PL and seal member 12 arepositioned over the shutter member 100 (as illustrated in dotted lines)the shutter member blocks the entire aperture of the seal member 12 toprevent liquid escaping through the aperture. In this position, thesubstrate W can be removed from the substrate table WT using usualsubstrate handling equipment. If the edge of the substrate W is close tothe edge of the shutter member 100 (i.e. the gap between the substrateW, when positioned on the pimple table or chuck or whatever holds thesubstrate W to the substrate table WT, and the edge of the shuttermember 100 is relatively small), there will be no sudden loss of liquidas the edge of the substrate moves under the aperture in the seal member12. The substrate table WT may be raised towards the projection systemto block the aperture so that the seal 16 can be deactivated.

Embodiment 2

A second embodiment is illustrated in FIG. 4 and allows the substratetable WT to be moved completely away from the projection system PL andseal member 12 in order for the substrate W to be removed from thesubstrate table WT and a new substrate to be placed on the substratetable WT. Thus it can be used, for example, with dual stage machines.

In the second embodiment, a shutter member 150 is in the form of a platewith a primary cross-sectional area larger than that of the localizedarea or aperture in the seal member 12. The shape of the shutter member150 may be any shape so long as it covers the aperture. The shuttermember 150 is not a substrate and is movable relative to both thesubstrate table WT and the seal member 12 and may be attached to theseal member 12 by any means, two examples of which are described below.

After imaging of the substrate W, the substrate table WT is moved sothat the shutter member 150 is positioned under the aperture of the sealmember 12. The gap between the substrate W and the top surface of thesubstrate table WT and the gap between the top of the substrate table WTand the top surface of the shutter member 150 are small so there is nocatastrophic loss of liquid from the reservoir 10 while passing over thegaps. The top (primary) surfaces (as illustrated) of the substrate W,substrate table WT between the substrate W and the shutter member 150and the shutter member 150 are arranged to be substantially co-planar.Once positioned under the projection system PL, the shutter member 150is attached to the bottom of the seal member 12 to cover the aperture.The seal member 12 is then moved away from the substrate table WT in theZ direction (the direction of the optical axis) or the substrate tableWT is lowered away from the seal member 12. The substrate table WT maythen be moved out of the way to a place where the substrate W may beexchanged. Once a new substrate has been loaded onto the substrate tableWT and any necessary alignment or other measurements (e.g. leveling)have been made (e.g. in a dual stage machine), the substrate table WT ismoved to a position where the shutter member 150 may be re-positionedonto the substrate table WT and then the substrate table WT is movedsuch that the substrate W is positioned under the projection system PLso that exposure can begin.

Of course it may be possible to provide the shutter member 150 on anobject in the lithographic apparatus other than the substrate table WT.For example, a robotic arm can be provided which moves to position theshutter member under the projection system after exposure.

The position of the shutter member 150 may drift over time so that meansfor centering or at least keeping a track of the position of the shuttermember is useful. This may be a mechanical or optical or electrical orother type of sensor on the landing area of the shutter member on thesubstrate table WT and/or such a sensor provided on the liquid supplysystem (e.g. seal member 12). For such a system, a quartz shutter memberis desired, especially for an apparatus which exposes at 193 nm,Alternatively or additionally, a through lens sensor and detector thatuses a reflected signal from a marker on the shutter member 150 whichsignal is coupled via a beam splitter to the detector is provided. Sucha system can be used while the substrate stage WT is moving, therebyimproving throughput. Alternatively or additionally, the position of theshutter member may be measured by an optical sensor on the substratetable WT. In this case a mark is applied to the underside or top side ofthe shutter member 150 (e.g. a transmissive pattern for the radiationwavelength) and the position of the shutter member 150 may then bemeasured by a sensor on the substrate table WT while the projectionsystem PL exposes the mark. The mark is transmissive to radiation fromthe projection system (or another radiation source) and a transmissionimage sensor (TIS) or spot-sensor which is on the substrate table WT canthen be used to measure displacement of the shutter member when attachedto the liquid supply system. Depending on the mark design on the shuttermember, the transmission image sensor (TIS) or spot sensor that isalready available in the substrate table WT can be used. In this way,the apparatus can keep a record of the drift in position of the shuttermember over time by sensing the position regularly, for example everycycle or perhaps only every ten or one hundred cycles or when is deemednecessary. Any necessary adjustments can then be made.

Alternatively, a quad cell sensor can be mounted at the center of theshutter member 150. An absorbing (or transmissive) spot is positioned inthe center of the mirror block so that when the shutter member 150 ispositioned on the substrate stage WT after use, its position can bemeasured. The quad cell sensor is made up of four light sensitive cellsin a square. When the light beam is on center the outputs of the fourcells are equal. If the sensor drifts to one side, the outputs of thecells on that side increase compared to the cells or the other side.Thus any deviation from the desired position can be corrected the nexttime the shutter member 150 is attached to the liquid supply system.

Another way of centering the shutter member 150, which does not involvecomplicated positional sensing, is to provide the shutter member 150with a shape which is self centering when picked up by the liquid supplysystem. A suitable example might be a thicker shutter member 150 than isneeded with a conical edge that locates in the aperture of the liquidsupply system.

FIG. 5 illustrates one way of attaching the shutter member 150 to theunderside of the seal member 12. This method usefully makes use of theseal 16 of the seal member 12. The outlet 14 is energized and the (gas)inlet 15 is not energized when the shutter member 150 is positionedunder the aperture. The vacuum provided in the outlet 14 is enough toattract the shutter member 150 to be clamped to the bottom of the sealmember 12 thereby sealing the aperture. When the shutter member 150 isreplaced on the substrate table WT, the seal 16 can be reactivated tooperate as normal and the substrate table WT moved to the exposeposition. The shutter member 150 may be held on the substrate table WTby use of vacuum outlet 157 connected to a vacuum source through a duct155. To avoid or reduce immersion liquid leakage under the shuttermember 150, a (annular) channel 158 is provided around the vacuum outlet157. The channel 158 is connected via a duct 159 to a vacuum source sothat any liquid is removed by the flow of gas through the channel 158caused by the vacuum. It might be advantageous to have a flow of gas inthe channel 158, even when the shutter member 150 is in place. To thisend a duct 156 open at a surface, for example the top surface of thesubstrate table WT, and connected to the channel 158 can be provided ona side substantially opposite to the duct 159 leading to the vacuumsource. In the second embodiment, the seal 16 need not be activatedwhile the shutter member 150 is positioned to cover the aperture but, inan embodiment, is activated.

An alternative means for holding the shutter member 150 to the substratetable WT and means for attaching the shutter member 150 to the sealmember 12, is illustrated in FIG. 6. In this embodiment the shuttermember 150 is made of a ferromagnetic material (or partly offerromagnetic material by making an assy) such that magnets 160, 170 (inan embodiment, electromagnets for easy attachment and detachment)positioned on the seal member 12 and substrate table WT may be used tohold the shutter member 150 in position against the seal member 12 andsubstrate table WT respectively. By keeping seal 16 activated, loss ofliquid can be minimized. The channel 158 and duct 156, 159 arrangementdescribed in relation to the FIG. 5 embodiment may also be employed inthe FIG. 6 embodiment to reduce or alleviate liquid leakage under theshutter member 150.

The shutter member 150 should be held by at least one of the substratetable WT and the seal member 12 so that the shutter member 150 is undercontrol.

As it is further illustrated in FIG. 6, it may be desirable to removeliquid 11 from the reservoir 10 during substrate exchange. This is doneby extracting the liquid either through the outlet 14 or the outlet duct13 (see, e.g., FIGS. 5 and 2 respective) and then flushing the spacewith gas provided through a further gas inlet 17. This might be done formaintenance and the lens may need to be cleaned after this process.

Of course, features from both FIGS. 5 and 6 can be combined.

Embodiment 3

A third embodiment is the same as the second embodiment except asdescribed below. The third embodiment is illustrated in FIG. 7 anddiffers from the second embodiment in that the shutter member 150 isplaced within the seal member 12. The similarity with the secondembodiment lies in the fact that the shutter member is separate from thesubstrate table WT. The shutter member 150 can be moved from any restingposition to block the aperture by being moved under the projectionsystem PL through channels 250 in the seal member 12.

The shutter member 150 may either be separate from the seal member 12and moved into the seal member 12 at the required time by a robotic arm,for example, or the shutter member may have a series of leafs 300 asillustrated in FIG. 8. The leafs 300 work like a shutter of a camera inthat the leafs can be moved such that they do not obstruct the aperturebut, when the plurality of leafs are moved to abut at the center of theaperture they thereby block the aperture.

Embodiment 4

A fourth embodiment is the same or similar as the second embodimentexcept as described below. The fourth embodiment is illustrated in FIGS.11 and 12. In this embodiment, the shutter member 150 is in the form ofa plate but the shutter member 150 does not come into contact with thebottom surface of the seal member 12. An advantage of not having theshutter member 150 come into contact with the seal member 12 is that iteliminates or at least reduces the chances of contaminating particlesbeing generated from contact of the shutter member 150 with the sealmember 12. Once positioned under the projection system PL, the shuttermember 150 is connected to the bottom of the seal member 12, as, forexample, implemented below, to cover the aperture in the seal member 12.

In an implementation, as shown in FIG. 11, the shutter member 150 isconnected to the underside of the seal member 12 using the seal 16 ofthe seal member 12. Both the outlet 14 and the (gas) inlet 15 remainenergized when the shutter member 150 is positioned under the aperture.However, the gas flow is adjusted so that there is enough vacuumprovided in the outlet 14 to attract the shutter member 150 toward thebottom of the seal member 12 but enough gas flow provided to inlet 15 tomaintain a gap between the bottom of the seal member 12 and the shuttermember 150. The gas flow in the seal 16 also can be sufficient toconfine the liquid 11 in the liquid reservoir 10 while the shuttermember 150 is connected to the seal member 12, When the shutter member150 is replaced on the substrate table WT or other location, the gasflow in the seal 16 can be re-adjusted to operate as normal so as torelease the shutter member 150.

In another implementation, as shown in FIG. 12, the shutter member 150may be made of a ferromagnetic material (or partly of ferromagneticmaterial) such that magnets 160 (in an embodiment, electromagnets foreasy connection and de-connection) positioned on the seal member 12 maybe used to connect the shutter member 150 to the seal member 12. In anexample, the attraction between the magnets 160 and the shutter member150 is configured so as to maintain a gap between the bottom of the sealmember 12 and the shutter member 150. Alternatively or in addition, thegas flow of seal 16 may be adjusted so as to maintain the gap betweenthe bottom of the seal member 12 and the shutter member 150. Whereliquid 11 is present in the liquid reservoir 10, the gas flow in theseal 16 also can be sufficient to confine the liquid 11 in the liquidreservoir 10 while the shutter member 150 is connected to the sealmember 12.

Referring to FIGS. 11 and 12, one or more projections 350 may beprovided on the seal member 12 to restrict the position of the shuttermember 150 in the X-Y plane. In a typical arrangement, a plurality ofprojections 350 are provided on the bottom surface of the seal member 12and are located such that they would be outward of the periphery of theshutter member 150 when the shutter member 150 is connected to the sealmember 12. The projection 350 may also be in the form a ring or otherperipheral arrangement that is outward of the periphery of the shuttermember 150 when the shutter member 150 is connected to the seal member12. In an embodiment, three projections 350 are provided in a triangularlayout to determine the shutter member 150 in the X-Y plane. In anembodiment, the projection(s) 350 is retractable so as to eliminate orat least reduce the chance that the projection(s) 350 deleteriouslycontacts the substrate table WT, the substrate or any other part of thelithographic apparatus.

Embodiment 5

FIGS. 13, 14 and 15 depict an embodiment of the shutter member 150 of,for example, any or all of the foregoing embodiments. In FIG. 14, theposition of the seal member 12 is generally shown by dashed lines.

In some situations, the liquid 11 in the liquid reservoir 10 maycomprise contaminating particles, such particles coming into the liquid,for example, through the physical contact of the seal member 12 and theshutter member 150. So, in a situation where the shutter member 150 isattached to or connected to the seal member 12 and the seal 16 ismaintained in whole (both gas supply and gas removal of the seal 16 areactivated) or in part (only gas removal of the seal 16 is activated),particles may be attracted to, and possibly trapped in, the innerinterface 420 between the seal member 12 and the shutter member 150 dueto liquid flow outwards caused by the gas removal of the seal 16 betweenthe shutter member 150 and the seal member 12.

So, in this embodiment, the shutter member 150 is provided with one ormore channels 400, the channels 400 being provided at least on theshutter member 150 at the location on the shutter member 150 of theinner interface 420 between the seal member 12 and the shutter member150. Through the use of channels, the contact area at the innerinterface 420 of the seal member 12 and the shutter member 150 can bereduced and thus, for example, reducing the chances of particles beingcreated through contact between the shutter member 150 and the sealmember 12. Further, liquid flow through the channels when the shuttermember 150 is connected to the seal member 12 can help to reducetrapping of particles that are smaller in diameter than the channeldepth and/or width.

In an implementation, the channels 400 are 1 to 10 micrometers deep.Where the shutter member 150 is attached to or connected to the sealmember 12 through the vacuum of the seal 16, the depth of the channelsshould be made such that enough vacuum remains to keep the shuttermember 150 in place.

In FIG. 13, the shutter member 150 is a circular disk and the channels400 are depicted as concentric circular channels provided only on theshutter member 150 in the general location on the shutter member 150 ofthe inner interface 420 between the seal member 12 and the shuttermember 150. In other implementations, the shutter member 150 and/or thechannels 400 may be in other shapes such as rectangular. Further, thechannels 400 may be provided over the entirety of the shutter member150.

In FIG. 14, the channels 400 are depicted having a rectangular profile.In an implementation, the channels 400 may have different profiles suchas semi-circular. Furthermore, the number of channels 400 may varyalthough in an embodiment, the number of channels is high, at least atthe inner interface 420, to promote greater flow and reduced contactarea.

In FIG. 15, the shutter member 150 is a circular disk and the channels400 are depicted as radial channels provided only on the shutter member150 in the general location on the shutter member 150 of the innerinterface 420 between the seal member 12 and the shutter member 150. Inother implementations, the shutter member 150 may be in another shapesuch as rectangular. Further, the channels 400 may be provided over theentirety of the shutter member 150. Also, as with FIG. 14, the profilemay have a rectangular or other different profile and the number ofchannels 400 may vary although in an embodiment, the number of channelsis high, at least at the inner interface 420, to promote greater flowand reduced contact area. Where, for example, a seal 16 is employed,with radial channels, a small liquid flow of liquid 11 towards the seal16 is provided. This liquid flow may rinse the shutter member 150 andprevent or reduce trapping of particles at interface 420 since theseparticles can be removed by the liquid or kept in the liquid.

In an embodiment, shutter member 150 contacts seal member 12 to positionseal member 150 in a horizontal plane. Alternatively, the shutter member150 may be displaced from seal member 12 as described above and someother means such as projections 350 may be used to keep shutter member150 in place.

In an embodiment, the channels may include projections (e.g., pimples)to provide mechanical connection of the shutter member 150 to the sealmember 12 and/or to prevent or reduce possible bending of the shuttermember 150.

Embodiment 6

Referring to FIG. 16, a simplified layout of part of an immersionlithographic projection apparatus is depicted according to an embodimentof the invention. In the layout, a projection system PL is connected toa projection system frame 500. The projection system frame 500 issupported on a base frame or ground 580 by a mount 530, 540, the mountcomprising a spring 530 and a projection system frame actuator 540. Inan embodiment, the mount may comprise a damper and one or more positionsensors to provide position information used to control the projectionsystem frame actuator 540. The projection system frame actuator 540 neednot be part of the mount and could be separately provided and connectedto the projection system frame 500. The projection system frame 500 isisolated from the base frame or ground 500 so that the projection systemPL can be kept substantially free from vibrations.

A member 520 (such as the seal member 12 described herein) of the liquidsupply system is connected to the projection system frame 500. In anembodiment, the member 520 is connected to the projection system frame500 by a liquid supply member actuator 510, which can displace themember 520 in a direction substantially parallel to the Z direction(e.g., the direction of the optical axis of the projection system PL).Alternatively or additionally, the member 520 may be flexibly connectedto the projection system frame 500 by a coupling (not shown). The partof the lithographic apparatus depicted in FIG. 15 further comprises asubstrate table WT, which in this case comprises a substrate holder 550supported by a substrate stage 570, the substrate holder 550 beingconnected and displaceable relative to the substrate stage 570 by asubstrate holder actuator 560. The substrate holder 550 holds asubstrate W (not shown). In an embodiment, the liquid supply memberactuator 510 and/or the substrate holder actuator 560 may have one ormore dampers associated therewith. Also, or alternatively, one or moreposition sensors may be provided to supply position information used tocontrol the liquid supply member actuator 510 and/or the substrateholder actuator 560. For example, an interferometer may be provided tomeasure the position of the substrate table WT with respect to theprojection system frame 500.

During exposure of the substrate W, the member 520 is supported on thesubstrate holder 550 (whether directly or indirectly via the substrateW) so that the weight of the member 520 is carried by the substrateholder 550 (and the substrate table WT generally) when no gravitycompensation of the member 520 is provided. Before or after exposure ofthe substrate W, the member 520 is displaced relative to the substrateholder 550 (e.g., by the liquid supply member actuator 510 displacingthe member 520 away from the substrate holder 550, by the substrateholder actuator 560 displacing the substrate holder 550 away from themember 520 or a combination of both) so that the substrate W can beremoved from or provided to the substrate holder 550 as appropriate.

The transfer of the weight of the member 520 between the substrateholder 550 and the projection system frame 500 may deform the relativelyweak springs 530 supporting at least part of the projection system frame500. Due to a very low stiffness of the projection system frame 500, theweight transfer may introduce a relatively large displacement andtemporarily instability of the system. Since the projection system frameactuator 540 typically has a low frequency, the projection system frameactuator 540 may not be able to compensate for the weight transfer intime resulting in a movement of the projection system frame 500. Suchmovement may cause measurement errors, exposure errors and/or failure,or any combination.

Accordingly, in an embodiment, the force for supporting the substrateholder 550 and the member 520 is measured or determined before themember 520 is displaced from the substrate holder 550. For example, theforce of the substrate holder actuator 560 used to support the substrateholder 550 and the member 520 may be measured. Similarly, the force forsupporting the member 520 is measured or determined before the member520 is displaced to the substrate holder 550. For example, the force ofthe liquid supply member actuator 510 used to hold the member 520 may bemeasured.

When the member 520 is displaced relative to the substrate holder 550 sothat the member 520 is no longer supported on the substrate holder 550,the force for keeping the substrate holder 550 in place (for example,the force of the substrate holder actuator 560) will decrease due to thereduction of weight. However, the force for supporting the projectionsystem frame 500, e.g., the force of the projection system frameactuator 540 used to support the projection system frame 500, willincrease by substantially the same amount as needed to support themember 520 on the substrate holder 550. So, to keep the projectionsystem frame 500 in place, the force of the projection system frameactuator 540, for example, should increase to prevent or at least reducethe projection system frame 500 from lowering due to the weight of themember 520 it now carries.

Similarly, when the member 520 is displaced relative to the substrateholder 550 so that the member 520 is supported on the substrate holder550, the force for holding the member 520 in place (for example, theforce of the liquid supply member actuator 510) will decrease due to thereduction of weight. So, the force for supporting the projection systemframe 500, e.g., the force of the projection system frame actuator 540used to support the projection system frame 500, will also decrease bysubstantially the same amount as needed to hold the member 520 onprojection system frame 500. So, to keep the projection system frame 500in place, the force of the projection system frame actuator 540, forexample, should decrease to prevent or at least reduce the projectionsystem frame 500 from raising due to the weight of the member 520 it nolonger carries.

The additional or reduced force needed, as appropriate, for theprojection system frame actuator 540, as an example, may be determinedfrom the change of force to support the substrate holder 550, e.g., thechange of force in the substrate holder actuator 560, and/or the changeof force to hold the member 520, e.g., the change of force in the liquidsupply member actuator 510. The change of force can be measured, forexample, by a force sensor. Alternatively or additionally, the change offorce can be determined from errors and corrections generated in thecontrol loops of any or all of the various actuators, e.g., theprojection system frame actuator 540, the liquid supply system actuator510 and/or the substrate holder actuator 560. The actuators then actessentially as a pair of scales to measure the weight of the part of theliquid supply system transferred between the projection system frame 500and the substrate table WT.

Alternatively or additionally, the additional or reduced force needed,as appropriate, may be determined from information about the weighttransfer between the projection system frame 500 and the substrate tableWT, including, for example, a calculation based on the mass of themember 520, the mass of the substrate holder 550, the mass of theprojection system frame 500 and/or other physical characteristics of thelithography apparatus.

In each circumstance, the change of force can be used in a feed-forwardor feedback manner. For example, the additional or reduced force for theprojection system frame actuator 540, derived, for example, from thechange of force in the substrate holder actuator 560 or the liquidsupply member actuator 510, can be fed forward to the projection systemframe actuator 540 so as to prevent or at least reduce the raising orlowering, as appropriate, of the projection system frame 500. Afeed-forward loop may prevent the projection system frame 500 fromlowering or raising since the feed-forward signal may be of relativelyhigh-frequency while the band-width of the projection system frameactuator 540 typically has a low frequency.

A controller (not shown) may be provided to obtain appropriatemeasurements and data (e.g., force measurements from a force sensorand/or data from actuator control loops) and to make the appropriatedeterminations (e.g., by calculation or table look-up) of a change offorce attributable to the weight transfer and/or the corresponding forceto be applied to the projection system frame 500 to compensate for theweight transfer. The controller may be electronic, mechanical, softwarebased, or any combination thereof. In an embodiment, the controller is asoftware program of the lithographic apparatus.

In short, the transfer of the weight of a part of the liquid supplysystem between the projection system frame 500 and the substrate tableWT can be determined and/or measured. A signal representative of theweight transfer can be fed forward (or fed back) into the control signalof the projection system frame mount 530,540 to prevent or at leastreduce low frequency movements of the projection system frame 500 havinglarge position overshoots, Advantageously, settling time for the systemmay be reduced and the stability of the projection system may beimproved.

The embodiments herein have been described in relation to the sealmember variant of the localized area solution. However, the embodimentsas described herein are equally applicable to any other type of liquidsupply for example those disclosed in European Patent application nos.03254078.3 or 03256643.2 hereby incorporated in their entirety byreference or to the variant illustrated in FIGS. 9 and 10. For example,in the case of a shutter member 150 moveable relative to both thesubstrate table WT and the projection system PL, means for attaching theshutter member below the in-and outlets IN, OUT may be attached to themembers forming the in-and-out-lets IN, OUT, or to a separate structure.Additionally or alternatively, the vacuum of the outlets OUT can be usedto attract the shutter member to the IN-and outlets IN, OUT and therebyseal the aperture. It may be desirable to use a non-flat shutter membere.g. one with a protruding border so that any drips of liquid from thevarious in-and out-lets are contained. Any system for generating a forcecan be used for the means for attaching, including low pressure sources,magnetic means, mechanical means, electro static means, etc.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

The invention claimed is:
 1. A lithographic projection apparatuscomprising: a substrate table by which a substrate is held; a projectionsystem by which a patterned beam is projected onto a target portion ofthe substrate, liquid being provided to a space between the projectionsystem and the substrate and being confined in said space by a sealmember; and a member having a first side and a second side opposite fromthe first side, the member being removably positionable adjacent to theprojection system between the projection system and the substrate tableso that the first side faces the projection system and the second sidefaces the substrate table to isolate the space provided with the liquidwhich contacts the first side of the member from a second space locatedon the second side of the member, wherein the member is separable fromthe substrate table and the projection system, and wherein the member ispositionable on the substrate table so that the first side issubstantially coplanar with a top surface of the substrate table thatreceives the substrate, wherein, in use, the liquid is at least partlyrecovered from underneath the seal member through a surface of the sealmember that faces the substrate, or the top surface of the substratetable or both.
 2. The apparatus according to claim 1, wherein the memberis positionable opposite the projection system such that liquid can beconfined between the projection system and the member.
 3. The apparatusaccording to claim 1, wherein the member is releasably connectable to anobject in the apparatus.
 4. The apparatus according to claim 3, furthercomprising a vacuum-clamp by which the member is releasably connectableto the object.
 5. The apparatus according to claim 1, wherein the memberis positionable on the substrate table so that the first side of themember is substantially coplanar with a primary surface of thesubstrate.
 6. A lithographic projection apparatus comprising: a supportstructure configured to hold a patterning device, the patterning deviceconfigured to pattern a beam of radiation according to a desiredpattern; a substrate table configured to hold a substrate; a projectionsystem configured to project the patterned beam onto a target portion ofthe substrate; a liquid supply system configured to provide liquid to aspace between the projection system and the substrate, the liquid supplysystem comprising a seal member that is configured to confine the liquidin said space; and a shutter configured to isolate the space from thesubstrate or a space to be occupied by a substrate, wherein the shutteris positionable on the substrate table so that a primary surface of theshutter is substantially coplanar with a top surface of the substratetable that receives the substrate, wherein, in use, the liquid is atleast partly recovered from underneath the seal member through a surfaceof the seal member that faces the substrate, or the top surface of thesubstrate table or both.
 7. The apparatus according to claim 6, whereinthe shutter is positionable on a side of the liquid supply systemopposite the projection system such that liquid can be confined in theliquid supply system and between the projection system and the shutter.8. The apparatus according to claim 6, wherein the shutter is releasablyconnectable to the liquid supply system.
 9. The apparatus according toclaim 8, wherein the shutter is separable from the remainder of theapparatus.
 10. The apparatus according to claim 8, wherein the shutteris displaced from the liquid supply system when connected to the liquidsupply system.
 11. The apparatus according to claim 10, comprising amagnet, a vacuum outlet, or both, configured to connect the shutter tothe liquid supply system.
 12. The apparatus according to claim 10,wherein the liquid supply system comprises a gas inlet and a vacuumoutlet configured to form a seal between the liquid supply system andthe shutter.
 13. The apparatus according to claim 6, wherein the shuttercomprises a channel in a surface of the shutter facing the projectionsystem.
 14. The apparatus according to claim 13, wherein the channel isless than or equal to 10 micrometers deep.
 15. The apparatus accordingto claim 13, wherein the shutter comprises a plurality of concentricchannels.
 16. The apparatus according to claim 13, wherein the shuttercomprises a plurality of radial channels.
 17. The apparatus according toclaim 6, wherein the liquid supply system comprises at least one inletto supply the liquid onto the substrate and at least one outlet toremove the liquid after the liquid has passed under the projectionsystem.
 18. The apparatus according to claim 6, wherein the liquidsupply system is configured to provide the liquid to a space between afinal lens of the projection system and the substrate.
 19. The apparatusaccording to claim 6, wherein the shutter is positionable on thesubstrate table so that the primary surface is substantially coplanarwith a primary surface of the substrate.